A brief description on a prior turbine airfoil and a film cooling hole in the prior turbine airfoil will be given hereinafter with reference to FIG. 13 and FIG. 14.
As shown in FIG. 13 and FIG. 14, the prior turbine airfoil is applied to a gas turbine engine of an aircraft engine or such and is comprised of a turbine airfoil main body 101 (shown only in part). Further, in portions (an airfoil for example) exposed to hot gas in the turbine airfoil main body 101, a plurality of film cooling holes 103 of a so-called shaped type, which expels cooling air CA, which is introduced from a side of an inner wall surface 101a of the turbine airfoil main body 101, along an outer wall surface 101b of the turbine airfoil main body 101, are formed by electric spark machining.
Further, a concrete constitution of the respective film cooling holes 103 is as follows.
More specifically, at a portion at the side of the inner wall surface 101a of the turbine airfoil main body 101, a straight hole portion 105 is formed and the straight hole portion 105 is so constituted that a cross section thereof is substantially uniform in shape along a thickness direction L1 of the turbine airfoil main body 101. Further, at a portion at the side of the outer wall surface 105b of the turbine airfoil main body 103, a diverging hole portion 107 continuous to the straight hole portion 105 is formed and the diverging hole portion 107 is so constituted as that a cross section thereof gradually broadens toward the side of the outer wall surface 101b of the turbine airfoil main body 101 and has an outlet surface 107p at a downstream side of the hot gas (the downstream side in view of a flow direction of the hot gas, at the right in FIG. 13 and FIG. 14). Further, each of the respective film cooling holes 103 is so constituted that the outlet surface 107p of the diverging hole portion 107 leans toward the downstream side of the hot gas on the basis of a hypothetical plane VP parallel to two directions of an axial center direction L2 and a lateral direction L3 of the straight hole portion 105.
In the meantime, an upstream end 107pu of the outlet surface 107p is disposed at a downstream side relative to an upstream end 107u of the diverging hole portion 107 at an aperture side, and a downstream end 107pd of the outlet surface 107p forms a downstream end of the diverging hole portion 107 at the aperture side.
Therefore, when the cooling air CA is introduced from the side of the inner wall surface 101a of the turbine airfoil main body 101 to the plurality of film cooling holes 103 under operation of the gas turbine engine, it expels cooling air CA along the outer wall surface 101b of the turbine airfoil main body 101 by means of the plurality of film cooling holes 103. Thereby, a film of the cooling air covering a wide range of the outer wall surface 101b of the turbine airfoil main body 101 can be generated and the turbine airfoil can be served with film cooling.